The role of ras (especially K-ras) and of neu in chemically induced tumors in rodents continues to be investigated in efforts to distinguish between activating mutations that are the direct result of chemical reactions of carcinogenic agents with DNA encoding these specific genes, and stochastic events that occur independently of the inducing carcinogen during tumor progression. Studies on rat renal mesenchymal tumors have been especially informative in this regard. A second theme has been extrapolation of activating mutational events in experimental tumors to human cancers that involve activation of the corresponding human oncogene; human pediatric renal tumor, as well as mucinous carcinoma of the ovary, endometrial carcinoma of the uterus, the "intestinal" variant of human gastric carcinomas and prostatic carcinoma are currently under investigation.